introduction

赝 Capacitor capacitor is a kind of energy storage device between battery and electric double layer capacitor. It realizes the storage of electrochemical energy through surface redox reaction or ion intercalation. The power density and cyclic stability have received more and more attention in recent years. MXenes is a two-dimensional layered carbide or nitride with a metal conductive core and a transition metal oxide-like surface. This special structure gives it ultra-high electrochemical performance. For example, Ti3C2Tx MXene hydrogel has a specific volume capacity. Up to 1500 F cm-3. But because MXene is easily oxidized, MXene and MXene-based composite materials can only be used as the negative electrode of supercapacitors.

Achievements

Recently, Professor Yury Gogotsi‘s team at Drexel University in the United States reported on a high-performance conductive polymer @carbide titanium MXene composite cathode material. The team of researchers first prepared a 3D Ti3C2Tx film using PS balls as a template. After casting polyaniline (PANI) and mechanical compression, a self-supporting PANI @ M-Ti3C2Tx composite film was obtained. Electrochemical tests have found that when Ti3C2Tx MXene is compounded with PANI or PEDOT: PSS, the electrochemical oxidation resistance of the composite film is significantly enhanced, which is mainly due to the increased stability caused by the higher work function of the composite material. In addition, due to the high specific capacity of PANI and the high conductivity of Ti3C2Tx, the PANI @ M-Ti3C2Tx composite cathode shows a record volume specific capacity in 3 M H2SO4 electrolyte (1632 F cm-3 at 10 mV s-1) And magnification performance (827 F cm-3 at 5000 mV s-1). Finally, the researchers constructed a super high performance asymmetric chirped capacitor using Ti3C2Tx (M-Ti3C2Tx) after compression as the negative electrode and PANI @ M-Ti3C2Tx as the positive electrode. The highest volume energy density and highest power density of the asymmetric capacitor are 50.6 Wh L-1 and 127 kW L-1, respectively. Related results were published in the journal "An Ultrafast Conducting Polymer @ MXene Positive Electrode with High Volumetric Capacitance for Advanced Asymmetric Supercapacitors", with the first authors Li Ke and Wang Xuehang.

Graphic guide

Figure 1. Schematic diagram of PANI @ M-Ti3C2Tx cathode preparation and related morphology and structure characterization

(a-f) Schematic diagram of the preparation of PANI @ M-Ti3C2Tx cathode;

(g) SEM image of Ti3C2Tx @ PS film;

(h) SEM image of 3D M-Ti3C2Tx film;

(i) SEM image of 3D PANI @ M-Ti3C2Tx thin film;

(j) 3D PANI @ M-Ti3C2Tx thin film EDS Mapping map;

(k) 3D PANI @ M-Ti3C2Tx thin film TEM image;

(i) SEM image of PANI @ M-Ti3C2Tx thin film.

Figure 2. Electrochemical performance of PANI @ M-Ti3C2Tx cathode

(a) CV curves of PANI @ M-Ti3C2Tx cathode at different scan rates;

(b) Rate performance of PANI @ M-Ti3C2Tx cathode with different loadings;

(c) PCD @ M-Ti3C2Tx GCD curve at positive maximum current density;

(d) b value of PANI @ M-Ti3C2Tx cathode with different loadings;

(e) Contribution of surface capacitance in PANI @ M-Ti3C2Tx positive electrode;

(f) PANI @ M-Ti3C2Tx EIS curve at different positive voltages.

Figure 3. DFT theoretical calculations

(a) reduced PANI structure;

(b) Ti3C2 (OH) 2 structure;

(c) Reduced PANI @ Ti3C2 (OH) 2 composite structure;

(d) Work functions of the three materials.

Figure 4.Electrochemical performance of asymmetric capacitors

(a) CV curve of M-Ti3C2Tx negative electrode and PANI @ M-Ti3C2Tx positive electrode;

(b) M-Ti3C2Tx // PANI @ M-Ti3C2Tx asymmetric capacitor CV curve;

(c) M-Ti3C2Tx // PANI @ M-Ti3C2Tx asymmetric capacitor GCD curve;

(d) Energy and power density of M-Ti3C2Tx // PANI @ M-Ti3C2Tx asymmetric capacitors with different loads

summary

In summary, the author has developed a high-performance positive electrode material of conductive polymer @carbide titanium MXene, and verified its higher electrochemical stability under forward voltage through first-principles calculations. Due to the high specific capacity of PANI and the high conductivity of MXene, the composite positive electrode exhibits ultra-high volume specific capacity (1632 F cm-3 at 10 mV s-1) and rate performance (827 F cm- at 5000 mV s-1 3). Asymmetric plutonium capacitors based on pure Ti3C2Tx negative electrode and PANI @ M-Ti3C2Tx composite positive electrode have a maximum volume energy density of 50.6 Wh L-1, even at an ultra-high power density of 127 kW L-1, the volume energy density still has 24.4 Wh L -1. This study shows that by combining MXene with a material with higher redox activity and higher work function, MXene can work stably under forward voltage. At the same time, the synergistic effect between the redox active material and MXene is beneficial to further enhance the comprehensive properties of the composite material. This research opens up a method for designing high-performance MXene-based composite cathode materials, and has certain guiding significance for the research in the field of electrochemical energy storage and conversion.

This article was contributed by the Yury Gogotsi team.

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